Though NavigatorContentUtils didn't have any scenario which can be shared across navigator instances, it has used RefCountedSupplement. So, we need to use Supplement<Page> instead of RefCountedSupplement<>.

(In reply to comment #0)
> Though NavigatorContentUtils didn't have any scenario which can be shared across navigator instances, it has used RefCountedSupplement. So, we need to use Supplement<Page> instead of RefCountedSupplement<>.
s/across navigator instances/across page instances/g
It was considered to make the NavigatorContentUtils shareable across navigator instances. However, it has used RefCountedSupplement<Page> instead of RefCountedSupplement<Navigator>.

(In reply to comment #3)
> (From update of attachment 230114[details])
> View in context: https://bugs.webkit.org/attachment.cgi?id=230114&action=review
>
> > Source/WebCore/Modules/navigatorcontentutils/NavigatorContentUtils.h:58
> > + static PassOwnPtr<NavigatorContentUtils> create(std::unique_ptr<NavigatorContentUtilsClient>);
>
> Should use std::unique_ptr, not PassOwnPtr, in new code. But I guess we need to fix all Supplement implementers at once.
Yes, I also wanna to it at once. I'm gonna file a bug for it.